HR: 15:00h
AN: T53D-06    [Abstracts]
TI: Non-uniform Extensional Processes Influenced by Fluid and Melt Distributions Below the Great Basin-Colorado Plateau Transition Zone, Utah, Revealed Through Electrical Conductivity Structure
AU: * Wannamaker, P E
EM: pewanna@egi.utah.edu
AF: University of Utah, Energy & Geoscience Inst. 423 Wakara Way, Ste 300, Salt Lake City, UT 84108 United States
AU: Hasterok, D P
EM: dhasterok@mines.utah.edu
AF: University of Utah, Dept. of Geology and Geophysics 717 W. B. Browning Bldg., Salt Lake City, UT 84112 United States
AU: Johnston, J M
EM: jeff@geometric.com
AF: Geometrics, Inc., 2190 Fortune Drive, San Jose, CA 95131 United States
AU: Sodergren, T L
EM: tsodergren@terratek.com
AF: TerraTek, Inc., 400 S Wakara Way, Salt Lake City, UT 84108 United States
AU: Doerner, W M
EM: Bill@quantecgeoscience.com
AF: Quantec Geoscience, 5301 Longley Lane, Ste 160, Reno, NV 89511 United States
AB: Electrical conductivity provides independent understanding of deep hydration, thermal regime, fluidization/melting, lithospheric-scale fabric and faulting, and economic resource controls. Since the early 1970's, regional conductivity surveys have shown a first-order partitioning of current activity in the Great Basin province, with the eastern and western margins being more anomalous w.r.t. a relatively quiescent Great Basin interior, in keeping with other indicators. The lower crust throughout the region is electrically conductive corresponding to a small fraction (less than 0.5%) of hypersaline fluids and silicic melts, thus implying weak rheology, but this is especially apparent in the active eastern Great Basin. The thermal profile of the central province lies near the ACMA geotherm below ~75 km, and the upper mantle there appears horizontally isotropic and only weakly hydrated at most. In contrast, eastern Great Basin upper mantle appears substantially hotter, with significant probable melting and an abrupt, non-uniform vs depth transition eastward to the stable Colorado Plateau. Within the transition zone itself, conductivity structures ressembling low angle detachments soling into a concentrated lower crustal conductor appear, with the latter interpreted to reflect ponded melts and exsolved fluids from basaltic underplating. Crustal-scale, steeply dipping conductive fault zones also appear in the province and may represent those where major deep earthquakes nucleate. Pre-Late Cenozoic heritage is revealed in detailed study of the Carlin Trend gold province, with a family of structures attributed to deep source rocks, Eocene intrusion, stratal deformation and alteration/graphitization. Lower crustal fabric inherited from the Proterozoic continental margin still appears to influence some deep electrical interconnection of fluids and melts today.
DE: 8102 Continental contractional orogenic belts
DE: 8159 Rheology--crust and lithosphere
DE: 7205 Continental crust (1242)
DE: 3630 Experimental mineralogy and petrology
DE: 3902 Creep and deformation
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting